Fuel injection pump

ABSTRACT

A fuel injection pump wherein the fuel distributing piston moves angularly and axially in synchronism with rotational speed of the engine and cooperates with an adjusting member which determines the beginning or termination of fuel injection into the cylinders. The adjusting member forms part of a transducer which is installed directly in the housing of the fuel injection pump and further includes an electromagnet having a rotary armature which is operatively connected with the adjusting member to position the latter in dependency on the intensity of signals which energize the electromagnet and are furnished by an electronic control circuit. The intensity of such signals, and hence the position of the armature, is a function of rotational speed of the engine, position of the gas pedal, and other factors.

United States Patent lll 3,630,643

[72] Inventors Franz Eheim 2,598,528 5/1952 French 123/139 E Stuttgart; 2,746,443 5/1956 Meyer.. 417/485 Kourld Eckert, Stuttgart-bad, Cannstatt; 2,889,780 6/ 1959 Binford 417/43 Gerald Hofer, Stuttgart, lll ofGennnny 2,937,637 5/1960 Heiser 417/494 [21] Appl. No. 12,409 3,064,579 11/1962 Staege et al 417/485 [22] Filed Feb. 18,1970 3,272,187 9/1966 Westbrook et al., 12S/139 E [45] Patented Dec. 28, 1971 3,371,610 5/1968 De Luca et al 417/485 [73 l Assignee unbe" Bouh Gmb Primary Examiner-Carlton R. Croyle suman Germany Assistant Examiner-John J, Vrablik [32] Pnomy Feb' 28 1969 Attorney-Michael S. Striker [33] Germany [31] P1910112.3

ABSTRACT: A fuel injection pump wherein the fuel distributing piston moves angularl and axiall in s nchronism [54] FUEL INJECTION PUMP with rotational speed of the engie and coopratesywith an ad- 15 chimsnnwing Figs justing member which determines the beginning or termina- [52] U.S. Cl 417/282, tion of fuel injection into the cylinders. The adjusting member 4l7/289,417/293,417/494, 123/32 AE,123/139E forms part of a transducer which is installed directly in the [51] lnt.Cl. .F04b 49/00, housing of the fuel injection pump and further includes an F04b 7/04, F04b 39/10 electromagnet having a rotary armature which is operatively [50] Fleld of Search 417/278, connected with the adjusting member to position the latter in 282,284, 289, 293,485,494, 498,499; 123/32 dependency on the intensity of signals which energize the AE, 139 E electromagnet and are furnished by an electronic control circuit. The intensity of such signals, and hence the position of [56] Referens Cited the armature, is a function of rotational speed of the engine,

UNITED STATES PATENTS position of the gas pedal, and other factors. 2,538,982 l/1951 Roosa i @masse a y, u

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sum u nf 4 FUEL INJECTION PUMP BACKGROUND OF THE INVENTION The present invention relates to fuel injection pumps for internal combustion engines in general, and more particularly to improvements in fuel injection pumps of the type wherein the amounts of fuel injected into the lcylinders of the engine are regulated by an electronic control circuit. Still more particularly, the invention relates to electronically controlled fuel injection pumps of the-type wherein a piston or an analogous fuel displacing and distributing member is either adjustable or cooperates with an adjusting member to determine the beginning and/or termination of fuel admission into the cylinders and to thus control the amounts of injected fuel.

Automotive vehicles wherein the cylinders of the engine receive metered quantities of fuel from an injection pump whole operation is regulated by an electronic control circuit must be equipped with transducers capable of converting electrical control signals into mechanical signals which are employed to adjust the pump as a function of factors which in fluence theoperation of the engine under a given set of circumstances or as a function of internationally created signals serving to insure that the engine is to operate in a certain way. Such mechanical signalscan be used to control'the timing of fuel injection and/or the quantities of injected fuel. For example, each cylinder of a'diesel engine must `receive metered quantities of fuel oil from a series injection pump or an injection pump utilizing a rotary fuel distributing piston. Electronic regulation of the fuel injection pump is particularly advantageous in a diesel engine because a single type of control circuit can be used to achieve any desired mode of operation with relatively minor outlays in electronic and electrical parts. Such control circuit .can insure that the operation of the engine is within an optimum range to thus avoid, for example, the generation of smoke as a result of admission of excessive amounts of fuel. Electronic control circuits can be used in practically all types of diesel engines because such circuits can be readily adapted to `be best suited for use with a particular type of engine. Mechanical controls are less flexible, i.e., they must be specifically designed for `various types of diesel engines, or the engine must be provided with complicated auxiliary equipment to permit the use of a standard mechanical controller.

lt was further found that the presently known transducers which convert the output signals of an electronic control circuit for the fuel injection pump in a diesel engine into mechanical signals have a relatively short useful life, mainly because diesel engines are preferred in trucks, tractors and like vehicles which are often subjected to extremely rough treatment. It is desirable to construct the electronic controls for a diesel engine in such a way that their useful life at least equals the useful life of the engine itself and the useful life of presently known mechanical controls. Also, the electronic controls and transducers therefor should not be prone to malfunction, i.e., they should be as sturdy and at least as reliable as purely mechanical controls. lt is normally expected that a vehicle which is driven by a diesel engine will be capable of travelling between 160,000 and 190,000 miles, and the electronic controls and transducers for use with the fuel injection pumps for such engines should be capable of operating satisfactorily during the entire useful life of the vehicle. Such requirements are not met by presently known electronic controls and transducers.

SUMMARY OF THE INVENTION An object of the invention is to provide a fuel injection pump wherein the quantity of injected fuel is regulated by a control circuit and wherein the transducer which adjusts the amounts of injected fuel in response to signals from the control circuit is sturdier and has a longer useful life than presently known transducers.

; Another object of the invention is to provide a fuel injection pump' for use in diesel engines wherein the transducer can stand exceptionally rough treatment andl is readily accessible for inspection, replacement or repair of its components.

A further object of the invention is to provide a` fuel injection pump wherein the transducer is automatically cooled and protected from external influences.

An additional object of the invention istoprovidea novel and improved electrical connection between the controlrcircuit and the transducer.

Still another object of the invention is to providenovelI feed' back signal generating devices forusein the improved'fuel'injection pump.

The invention is embodied ina fuel injection pump for-internal combustion engines, particularly for diesel engines, which comprises a housing, .an engine-driven distributing member which is installed in the housing and servestto admit metered quantities of fuel to the cylinders of the enginefa control circuit arranged to produce control signals whose characteristics vary at least as a function of .changes in rotational speed of the engine, and transducermeans provideddirectly in the housing and responsive to the control signals :to influence the distribution of fuel bythe distributormembertfor example, by determining rthe beginning or the `termination 'of fuel injection). The transducer v-means comprises an electromagnet which is energizable bythe controlsignals andvhas a rotary armature whose angularposition is a function of `the characteristics of control signals.

In accordance with a more specific feature of the invention, the transducer means further comprises a shaft `.which is rotatable with the armature, an eccentric mounted yon the shaft, a collar surrounding and Amovable axially ofthe :distributing member to thereby influence the distribution of vfuel to the cylinders, and a ball-.and-socket connection betwee the collar and the eccentric.

The novel features which are considered as characteristic/of the invention are set forth in particular 'in the appende claims.

The improved fuel injection pump itself, however, both as to its construction and .its mode of operation, together with additional features and advantages thereof, will lbe Abest understood upon perusal of the following detailed description of certain specific embodiments with reference to the yaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. l is a schematic partly sectional view of certain elements in a fuel injection pump which embodies the invention;

FIG. la shows parts of the electromagnet and of a feedback signal generator in the pump housing;

FIG. 1b shows parts of a feedback signal generator;

FIG. 2 is a longitudinal vertical sectional view of the pump;

FIG. 3 is a plan view of the pump, with the cover of the pump housing removed; and

FIG. 4 is a diagrammatic bottom plan view of the cover.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring first to FIG. l, the numeral 10 denotes the rotary armature of an electromagnet which forms part of a novel transducer and further includes stationary windings 11 and 12. These windings are convoluted onto a core 13 in such a way that a closed magnetic circuit is established on completion of the circuit The armature 10 is secured to a shaft 14 which is journaled in a part l5 constituting a component of the housing of the fuel injection pump. The lower end of the shaft 14 (as viewed in the lower half of FIG. 1) carries an eccentrically mounted segment 16 having a spherical motion transmitting element 17 (hereinafter called ball) which is received in a cylindrical socket 18 provided on a collar 19 axially movably surrounding a portion of a fuel distributing piston 20. The latter is provided with a channel 21 for admission of fuel to fuel lines 25 for individual cylinders of the engine. Depending on its axial position, the collar 19 can cover or expose larger or smaller portions of the intake ends of the channel 21 in various axial positions of the piston 20. This piston is biased by a spring 22 which urges it against a disk 23 serving to move the piston axially and angularly and receiving motion from the output shaft 50 (FIG. 2) of the internal combustion engine. Though FIG. 1 shows a single fuel line 25, it is clear that the piston 20 can regulate the timing and rate of admission of fuel to two or more fuel lines.

The output shaft 50 of the engine is coaxial with the piston 20 and is connected with a gear 30 which is adjacent to the yoke 31 of a feedback signal generator and establishes therewith a magnetic circuit wherein the magnetic flux pulsates at a rate which is a function of rotational speed of the gear 30. An induction coil 32 on the yoke 31 produces voltage pulses in response to changes in magnetic flux. The yoke 3l comprises two-toothed or serrated portions 31a, 31b which are adjacent to the teeth of gear 30.

When the circuit of the windings 11, 12 is open, the armature 10 is held in a predetermined starting position by biasing means here shown as a helical return spring 33. The angular position of the armature l is a function of energization of the electromagnet and this armature carries an actuator or cam 34 which determines the condition of an inductive feedback signal generator 53. The signal generator 53 includes two series-connected annular inductances 35, 36 which surround an axially reciprocable core 37 of ferrite or like ferromagnetic material. A pusher 38 serves as a means to transmit motion from the cam 34 to the core 37. The reproducibility of the feedback signal from the signal generator S3 is enhanced by the provision of a spring 3,9 which biases the core 37 against the pusher 38 and the latter against the cam 34.

The windings 11, 12 of the electromagnet are connected in series and receive current from an amplifier 41 which preferably includes commercially available prefabricated semiconductor blocks. The amplifier 4l is connected with the output of an electronic control circuit 42 whose input or inputs are directly or indirectly connected with conventional means for transmitting signals which indicate various factors influencing the operation of the internal combustion engine. Such factors include the feedback signals furnished by the generator 53 (which is supplied with alternating current by an oscillator circuit 43) as well as the feedback signals furnished by the induction coil 32 as a function of rotational speed ofthe shaft S0. The control circuit 42 is further connected with a transducer 44 which produces an input signal indicating, for example, the position of the gas pedal, the pressure in the intake manifold, the temperature of the engine and/or the at mospheric pressure. The arrow 45 indicates the connection between the transducer 44 and a device which can produce signals 0f varying magnitude, for example, the connection with the gas pedal.

The parts -14 and 16-19 constitute a novel transducer which serves to influence the distribution of fuel by the piston in dependency on the characteristics of control signals furnished to the electromagnet 10-13 bythe circuit 42 by way of the amplifier 41.

The cam 34 can be replaced by a pinion and the pusher 38 is then replaced with a rack which meshes with the pinion and can move the core 37 against the opposition ofthe spring 39.

The operation:

The control signal furnished by the circuit 42 is a function of the position of the gas pedal (arrow 45) as well as of certain other factors which influence the transducer 44, of the feedback signal furnished by the coil 32, and of the feedback signal furnished by the signal generator 53. The amplifier 41 transmits such control signal to the windings 11, 12 which influence the angular position of the armature 10 and hence the axial position of the sleeve 19 with reference to the piston 20. Changes in angular position of the armature 10 are communicated to the control circuit 42 by way ofthe signal generator 53. The adjustment ofthe armature l0 and the indication of itsjposition to the control circuit 42 are preferably carried out in such a way that the feedback signal from the signal generator 53 modifies the control signal from the circuit 42. This insures that the angular position of the amature l0 is not unduly affected by friction` shocks and other undesirable influences. The armature l0 adjusts the sleeve 19 by way of the eccentric 16 and ball-and-socket connection 17-18. The sleeve 19 in turn influences the timing of bypassing of fuel to chamber 72 through the channel 21 in the piston 20 which rotates and moves axially when the shaft 50 is driven by the engine. Thus, the sleeve 19 influences the amounts of fuel which are pumped into the fuel lines 25 so that such amounts are a function of angular position of the armature 10. The manner in which the shaft 50 drives and reciprocates the piston 20 is fully disclosed, for example, in U.S. Pat. No. 3,333,542 to Eheim which is assigned to the same assignee. The spring 22 insures that the face 23a of the disk 23 cannot move away from idler rollers 51 (FIG. 2) which cause the disk 23 to move axially in response to rotation with the shaft 50.

FIG. 2 illustrates in greater detail the construction of a fuel injection pump which embodies the features of the structure shown in FIG. 1. The output shaft 50 of the internal combustion engine is coupled for rotation with the disk 23 by way of keys 50a which enable the disk 23 to move axially (under or against the bias of the spring 22), and the face 23a of the disk 23 engages several idler rollers 51 in the pump housing whereby the configuration of the face 23a determines the extent of axial movement of the piston 20. The operative connection between the adjusting collar 19 and the armature l0 of the first electromagnet is the same as that shown in FIG. l. The parts 19, 20 are accommodated in a high-pressure chamber 72, which can discharge fuel through passages defined by a filter 52. The latter separates the chamber 72 from a compartment 75 which accommodates the electromagnet including the armature l0, windings l1, 12 and core 13. The piston 20 draws fuel from the chamber 72 and the filter 52 insures that metallic shavings or other magnetizable impurities which might be contained in the compartment 72 cannot enter the chamber 75 and there disturb the proper function of the rotary armature 10 by being attracted by one of the windings 11, l2. Such foreign matter could interfere with proper metering and distribution of fuel to the lines 25. The chamber 72 is large enough to accommodate much more fuel than necessary for introduction into the fuel lines 25. The surplus fuel is withdrawn from the compartment 75 which further accommodates the feedback signal generator 53 (containing the parts 35-38 of FIG. l). ln this way the electromagnet and the feedback signal generator 53 are effectively cooled by the circulating fuel.

The yoke 3l which carries the induction coil 32 is mounted on a supporting bracket 54 provided with elastic contacts 55 which are connected with the ends of the coil 32. A separable cover or lid 56 of the pump housing comprises an extension 57 constituting a socket for insertion of a plug whose contacts then engage the terminals 6l in the socket 57 and which connects the electromagnet and the signal generators with the control circuit 42. An insulating support plate 58 at the inner side of the cover 56 is provided with a printed circuit certain conductors of which are in contact with the contacts 55 when the cover is properly secured to the main portion of the pump housing. The plate 58 further carries elastic contacts 59 which engage the ends of windings ll, l2 to establish the connection between the amplifier 41 (not shown in FIG. 2) and the electromagnet (in the compartment 75). lt is preferred to provide on the plate 58 all such conductors which connect the electrical parts in the pump housing with electrical and electronic parts located externally of the fuel injection pump. The character 60 denotes pin-shaped terminals which are connected with the conductors on the plate 58 and are embedded in droplets of glass to insure satisfactory resistance to ternperature and pressures. The terminals 60 extend upwardly into the socket 57 and are electrically connected with the terminals 61. The connection between the terminals 60, 61 is embedded in a mass 62 of heat-resistant insulating material. Such mass holds the terminals 61 against uncontrolled movement and stabilizes the terminals 60 on the support plate 58. The

operation of the pump shown in FIG. 2 is identical with that of the structure illustrated in FIG. l.

FIG. 2 further shows a fuel source or tank 71 which is connected with an inlet of the chamber 72 by way of a fuel circulating pump 73, a return conduit 74 which connects the tank 71 with the compartment 75 and contains a flow restrictor 76, and an adjustable relief valve 77 which determines the pressure of fuel in the chamber 72. The pump 73 is driven by the engine and circulates fuel in such quantities that fuel flows from the chamber 72, through the passages defined by filter 52, through the compartment 75, conduit 74 and back to the tank.

FIG. 3 illustrates the fuel injection pump of FIG. 2 in plan view but with the cover 56 detached from the main portion 80. It will be seen that the supporting bracket 54 is bolted or screwed to the pump body and that its elastic contacts 55 are positioned in such a way that they are automatically engaged by the corresponding parts of the printed circuit when the cover 56 is secured in position. The numeral 68 denotes a counterpoise which is located above the cam 34 and return spring 33. The cam 34 engages the pusher 38 of the feedback signal generator 53 whose casing is provided with three contact surfaces 69 engaging with elastic contacts 59 on the support plate S8 when the cover S6 is properly secured to the main portion 80 of the pump housing. Springy contacts 63 supply current to the ends of the windings 11, 12. The counterpoise 68 balances the weight o'f the eccentric 16; these parts are mounted at the opposite ends of the shaft 14. The spring 33 engages a pin 81 on the counterpoise 68 and the latter is adjustable with reference to the shaft 14 on loosening of a screw 82. Stops (one shown at 83) are provided to limit the extent of angular movement of the armature l0 and hence the extent ofaxial movement ofthe adjusting collar 19.

FIG. 4 illustrates the insulating support plate 58 at the underside ofthe cover 56. The details ofthe printed circuit at the underside of the plate 58 are clearly visible, together with elastic contacts 59. FIG. 4 further shows the recess of the socket 57 with terminals 61 and the connections between the terminals 60 on the support plate 58 and terminals 61.

An advantage of the cover 56 and support plate 58 is that the contacts 55, 63, 69 in the pump housing proper can be rapidly connected to and disconnected from the terminals 61 as well as that the parts in the compartment 75 are fully accessible upon detachment of the cover 56. The contacts in the compartment 75 and the corresponding parts of the circuit on the support plate 58 are preferably coated with layers containing noble metals or other suitable corrosion-resistant materials.

lt is further clear that the above-described features can be embodied in other types of pumps without departing from the spirit of our invention. For example, the invention can be embodied in a series injection pump; the control rod of such series injection pump is then moved by the rotary armature of an electromagnet which is energized in the same way as described in connection with FIG. l.

A control circuit which can be used with the fuel injection pump of our invention is disclosed, for example, in the VGerman Pat. No. 1,264,142.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features which fairly constitute essential characteristics of the generic and specific aspects of our contribution to the art and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

We claim:

1. A fuel injection pump for internal combustion engines, comprising a housing; an engine-driven fuel distributing member provided in said housing; a control circuit arranged to produce control signals whose characteristics vary at least as a function of changes in rotational speedfo'f the engine; and transducer means provided in said housing and responsive `to said control signals to influence the distributionof fuel by `said member, said transducer means comprising an electromagnet energizable by said control signals and having a rotaryarmature whose angular position is a function of the characteristics of said control signals.

2. A pump as defined in claim l, further comprising stop means for limiting the extent of rotary movement of said .armature.

3. A pump as defined in claim 1, further comprising means for supplying to said control circuit feedback signals whose characteristics vary as a function of changes in rotational speed of the engine, including a gear driven by the engine, a magnetic yoke having at least one serrated portion adjacentto said gear, and an induction coil provided on said yoke and electrically connected with said control circuit.

4. A pump as defined in claim 1, wherein said housing is provided with a fuel-filled chamber for said distributing member and with a fuel-filled compartment for said electromagnet, and further comprising filter means providing passages for the flow of fuel from said chamber to said compartment, a source of fuel, and rmeans for circulating fuel from said source to said chamber at such a rate that surplus fuel not distributed by said distributing member passes through said filter means, through said compartment and back to said source.

5. A pump as defined in claim l, wherein said housing comprises a main portion and cover means separably secured Vto said main portion and having socket means provided with terminals connected with said control circuit, and further comprising an insulating support provided `at that side of said cover means which is concealed when the latter is secured to said main portion, conductors provided on said support and connected with said terminals, and contact means establishing a separable electrical connection between said conductors and said transducer means.

6. A pump as defined in claim 5, wherein said conductors include second terminals embedded in vitreous material and further comprisingfconnections between said second terminals and the terminals of said socket and a mass of heat-resistant insulating material surrounding said connections.

7. A pump as defined in claim l, wherein -said transducer means further comprises a shaft rotatable with said armature, an eccentric on said shaft, a collar surrounding and movable axially of said distributing member, and a ball-and-socket connection between said collar and said eccentric.

8. A pump as defined in claim 7, wherein said distributing member is a piston and further comprising means for effecting axial and angular movements of said piston in Asynchronism with rotational speed of the engine.

9. A pump as defined in claim 7, wherein said eccentric is provided at one end of said shaft and said transducer means further comprises a counterpoise provided at the other end of said shaft to balance the weight of said eccentric.

l0. A pump as defined in claim 9, wherein said counterpoise is adjustable with reference to said shaft.

l1. A pump as defined in claim 9, further comprising lbiasing means for urging said armature to a predetermined starting position in which said armature remains when said electromagnet is deenergized.

12. A pump as defined in claim 11, wherein said biasing means comprises a spring connected to said counterpoise.

13. A pump as defined in claim l, further comprising an inductive feedback signal generator arranged to furnish `to said control circuit feedback signals indicative of the angular position of said armature.

14. A pump as defined in claim 13, wherein said signal generator comprises two series-connected annular inductances connected with said control circuit, a ferromagnetic core movable axially of said inductances, and means for shifting said core in response to changes in the angular position of said armature.

l5. A pump as defined in claim 14, wherein said signal generator further comprises resilient means arranged to yieldably oppose axial movement of said core in one direction.

* lll Il 

1. A fuel injection pump for internal combustion engines, comprising a housing; an engine-driven fuel distributing member provided in said housing; a control circuit arranged to produce control signals whose characteristics vary at least as a function of changes in rotational speed of the engine; and transducer means provided in said housing and responsive to said control signals to influence the distribution of fuel by said member, said transducer means comprising an electromagnet energizable by said control signals and having a rotary armature whose angular position is a function of the characteristics of said control signals.
 2. A pump as defined in claim 1, further comprising stop means for limiting the extent of rotary movement of said armature.
 3. A pump as defined in claim 1, further comprising means for supplying to said control circuit feedback signals whose characteristics vary as a function of changes in rotational speed of the engine, including a gear driven by the engine, a magnetic yoke having at least one serrated portion adjacent to said gear, and an induction coil provided on said yoke and electrically connected with said control circuit.
 4. A pump as defined in claim 1, wherein said housing is provided with a fuel-filled chamber for said distributing member and with a fuel-filled compartment for said electromagnet, and further comprising filter means providing passages for the flow of fuel from said chamber to said compartment, a source of fuel, and means for circulating fuel from said source to said chamber at such a rate that surplus fuel not distributed by said distributing member passes through said filter means, through said compartment and back to said source.
 5. A pump as defined in claim 1, wherein said housing comprises a main portion and cover means separably secured to said main portion and having socket means provided with terminals connected with said control circuit, and further comprising an insulating support provided at that side of said cover means which is concealed when the latter is secured to said main portion, conductors provided on said support and connected with said terminals, and contact means establishing a separable electrical connection between said conductors and said transducer means.
 6. A pump as defined in claim 5, wherein said conductors include second terminals embedded in vitreous material and further comprising connections between said second terminals and the terminals of said socket and a mass of heat-resistant insulating material surrounding said connections.
 7. A pump as defined in claim 1, wherein said transducer means further comprises a shaft rotatable with said armature, an eccentric on said shaft, a collar surrounding and movable axially of said distributing member, and a ball-and-socket connection between said collar and said eccentric.
 8. A pump as defined in claim 7, wherein said distributing member is a piston and further comprising means for effecting axial and angular movements of said piston in synchronism with rotational speed of the engine.
 9. A pump as defined in claim 7, wherein said eccentric is provided at one end of said shaft and said transducer means further comprises a counterpoise provided at the other end of said shaft to balance the weight of said eccentric.
 10. A pump as defined in claim 9, wherein said counterpoise is adjustable with reference to said shaft.
 11. A pump as defined in claim 9, further comprising biasing means for urging said armature to a predetermined starting position in which said armature remains when said electromagnet is deenergized.
 12. A pump as defined in claim 11, wherein said biasing means comprises a spring connected to said counterpoise.
 13. A pump as defined in claim 1, further comprising an inductive feedback signal generator arranged to furnish to said control circuit feedback signals indicative of the angular position of said armature.
 14. A pump as defined in claim 13, wherein said signal generator comprises two series-connected annular inductances connected with said control circuit, a ferromagnetic core movable axially of said inductances, and means for shifting said core in response to changes in the angular position of said armature.
 15. A pump as defined in claim 14, wherein said signal generator further comprises resilient means arranged to yieldably oppose axial movement of said core in one direction. 